This invention concerns a harvesting or gathering platform for the header of a harvester and especially a platform equipped with a flexible floating cutterbar.
Flexible cutting platforms are well known. Typically, they are part of a forward mounted header of a self-propelled harvester such as a combine. They are particularly useful when harvesting efficiency depends on cutting a crop (such as soybeans) uniformly close to the ground along the length of the cutterbar. Such a platform is described in some detail in U.S. Pat. No. 3,982,383, Mott sharing an assignee with the present application.
To facilitate cutting close to the ground, the cutterbar is connected so that it may float vertically relative to the platform. Typically, some form of spring is provided in the suspension of the cutterbar as a counterbalance to reduce the ground pressure of a shoe or skid plate of the cutterbar assembly so as to avoid "bulldozing" of the ground surface or dragging of crop material.
In a common flotation arrangement (see, for example, U.S. Pat. No. 3,886,718 Talbot) rearwardly extending cutterbar support arms are pivotally attached to the underside of the platform and are biased upwards by a leaf spring between each arm and the platform. Counterbalance force can be adjusted only by manipulation of a clip securing the spring to the support arm under the platform, an inconvenient location. In another arrangement, where cutterbar movement is also essentially pivoting about a single rearwardly disposed pivot under the platform, the upward bias of the cutterbar comes from a compression spring behind the rear wall of the platform. These springs are more accessible for adjustment but adjustment of the platform float pressure depends on separate adjustment of a plurality of springs and friction in the spring linkage makes float pressure somewhat unpredictable (see U.S. Pat. No. 4,206,583 Week). In '383 Mott, the thin sheet metal apron or feed plate extending between the cutterbar and the fixed portion of the platform floor is mounted so that it serves as a counterbalance spring as well as a floor portion but is essentially nonadjustable.
Conventionally, a fairly generous vertical or up and down flotation range of the cutterbar relative to the platform floor is provided by the suspension arrangements. Thus, by adjusting the vertical position above the ground of the header and hence of the rigid portion of the platform, an operator chooses a nominal operating condition in which the cutterbar is floating in a particular portion of the total flotation range. In most conventional arrangements, the operator must accept a change of cutterbar ground pressure when he changes platform height because of the related change in counterbalance spring deflection. (It must be noted however, that Week claims a linkage arrangement which makes counterbalance force independent of position in the flotation range.)
Thus, of the cutterbar flotation adjustment arrangements known, all are relatively inconvenient and none lends itself to convenient on-the-go adjustment of cutterbar ground pressure. Most, if not all, have the undesirable characteristic of ground pressure varying with up and down displacement of the cutterbar relative to the platform.
The use of an approximately parallel linkage suspension for the cutterbar, as in Mott, is advantageous in ensuring that cutterbar attitude remains in a desirable range while floating. The linkage is attached to the underside of the platform by a frame member tied to a rigid floor portion. However, occasional necessary adjustment of the basic cutterbar attitude involves a flexing of the platform floor which is undesirable.